Class 12 Physics practical reading To draw the characteristic curve of a p-n junction in forward and reverse bias.

Aim

To draw the characteristic curve of a p-n junction in forward and reverse bias.

Apparatus Required

A junction diode (IN 270 or IN 3065), milliammeter (0 - 500 mA), voltmeter (0 - 3V), microammeter (0- 100 µA), volmeter (0 – 100 V), 5 V and 100 V d.c. supplies, rheostat, key and connecting wire (or a diode characterization box)

Theory

Biasing of P-N Junction Diode
Forward Biasing- When a battery is connected to a p-n junction diode in such a way that the positive terminal of the battery is connected to the p-side and the negative terminal to the n-side, the junction diode is said to be forward biased. A forward biased junction diode is shown in Fig.

Reverse Biasing - When a battery is connected to p-n junction diode in such a way that the positive terminal of the battery is connected to n-side and the negative terminal to the p-side, the junction diode is said to be reverse biased. A reverse biased junction diode is shown in Fig.

Procedure

Forward Bias characteristics:

1. Connect the junction diode in forward biased mode using the circuit diagram in fig

 2. Adjust the position of the variable contact of the rheostat so that initially the voltmeter shows zero. Now, in- crease the voltage in steps of 0.1 V and record the voltmeter and milliammeter readings in the observation table. 

Reverse Bias Characteristics : 

3. Connect the junction diode in reverse bias mode using the circuit diagram shown in Fig. 

4. Starting from zero volt, increase the reverse bias potential in steps of 1V. Record the voltmeter and micro-ammeter readings in the observation table. Normally, the applied reverse bias should not exceed breakdown voltage of the diode, therefore stop as soon as there is large increase in current. Draw forward bias characteristic curve taking voltage along + X-axis and current along + Y-axis, and reverse bias characteristic curve taking voltage along – X-axis and current along - Y-axis.

Observations & Calculations

Precautions

1. In forward bias condition, initially adjust rheostat position so that voltmeter reading is zero. Then, increase the voltages in the steps of 0.1 V. 

2. In reverse bias, as higher biasing is used, initially adjust the voltage at 0.5 V and then increase the voltage in steps of 1 V. 

3. Unless permitted by your teacher, do not increase the reverse bias so much that diode undergoes breakdown a it may damage the diode.